Blood flow and rate of oxygen consumption are closely matched in vivo under normal conditions. Coronary flow is regulated through the combined action of metabolic, adrenergic, and mechanical (myogenic and shear) mechanisms. Since vascular mechanical processes are linked to the mechanics of cardiac contraction, understanding flow regulation requires a model that accounts for mechanics from the microvessel to the whole-organ level. Accordingly, the overall objective of this grant is to develop a validated multi-scale model of coronary autoregulation that accounts for the various major determinants of coronary flow regulation. To accomplish this goal, we set the following three Specific Aims: Aim 1: To construct a multi-scale mechanistic model of coronary flow regulation integrating cell-level models of endothelial and smooth-muscle function, single-vessel mechanics of coronary resistance arteries, autonomic function, network-level myocardium- coronary vessel interaction and conducted metabolic response; Aim 2: To validate the ability of the model of Aim 1 to predict physiological dynamics observed in the awake exercising pig; and Aim 3: To use the models from Aim 1, refined by data from Aim 2 to understand the multiscale effects of stenosis on pulsatile flow in coronary arteries. We will test the hypothesis that the multiple parallel control mechanisms fail when coronary arteries become stenotic because they act out of sync and interfere. The model predictions will be compared to data from three complimentary protocols: (1) dynamic measurements of flow, pressure, and diameter in coronary arteries ranging from 50 mm to the large epicardial vessels; (2) steady-state measurements of venous (coronary sinus) pO2 versus left-ventricular oxygen consumption in different exercise states; and (3) measurement of the dynamic reactive hyperemic response flow following acute transient occlusion of the left anterior descending coronary artery. Protocols will be conducted with and without specific pharmacological interventions to inhibit receptors and channels represented in the cell-level models. The validated model will be used to investigate critical questions, including: What is the principle mechanism coupling coronary blood flow to metabolism in vivo? How is high resting oxygen extraction functionally linked to the ability of the system to effectively respond to increased demand in exercise?